1. Field of the Invention
The present invention relates to a method for producing a powdery solid of Dunaliella algae containing β-carotene at a high concentration.
2. Description of the Related Art
In general, β-carotene is a representative oil-soluble organic compound of carotenoids contained in brightly colored vegetables such as a carrot, is known to be degraded into retinal by an enzyme and then oxidized into vitamin A (retinol) in a body, and is a useful compound for a human body. Furthermore, a retinoic acid obtained by further oxidization of retinol has been reported to have an anticancer activity, and therefore much more attention has been focused on β-carotene.
As a method for producing β-carotene, a production method from β-ionone by chemical synthesis and a production method by culturing algae such as Dunaliella algae, Spirulina algae, and Chlorella algae are known. Recently, since consumers have been becoming nature-oriented, β-carotene derived from chemical synthesis may be avoided, and therefore β-carotene derived from natural products obtained by, for example, culturing algae has been demanded.
As microalgae having a high content of β-carotene derived from natural products, Dunaliella is known. The algae belonging to the genus Dunaliella are salt-tolerant single cell green algae belonging to the phylum Chlorophyta, the class Chlorophyceae, the order Volvocales, and the genus Dunaliella, and are known to inhabit the Dead Sea, Israel, and Great Salt Lake, Utah, USA.
In order that a consumer can easily take or store β-carotene, a dried powder of Dunaliella algae, a tablet obtained by compressing and hardening the dried powder of Dunaliella algae, or a capsule obtained by encapsulating the dried powder of Dunaliella algae are known. In any states, firstly, it is necessary to dry a culture solution of Dunaliella algae and to form it into dried powder.
For example, Japanese Patent Laid-Open No. 1997-203 discloses that a dried powder product of the algae belonging to the genus Dunaliella is obtained by previously decreasing the water content of a culture solution of cultured Dunaliella alga body to, preferably, about 50% for easy drying, followed by being subjected to nebulization drying, vacuum drying or freeze drying.
Furthermore, Japanese Patent Laid-Open No. 2001-161348 discloses that a dried powder product of the algae belonging to the genus Chlorella is obtained by dehydrating a suspension of mass cultured chlorella by centrifugation and treating the dehydrated product in a solution of pH 5.5 containing an enzyme or polysaccharides, followed by heating and cooling and then lyophilization.
Dried powder products of the algae belonging to the genus Dunaliella are sold as foods. It is necessary to carry out a step of decreasing compounds that may be harmful to a human body in a step of producing a dried powder product from the harvested algae belonging to the genus Dunaliella in order to satisfy a predetermined safety standard.
Among others, a part of algae such as the algae belonging to the genus Dunaliella contains pheophorbide. Pheophorbide is hygienically harmful and causes skin disorder. Specifically, as described in the attached document to “Regarding Prevention of Hygienic Harm by Chlorella Containing Chlorophyll Degradation Products such as Pheophorbide” (May 8, 1981, Kanshoku No. 99, Notification of the Director of Environmental Health Bureau of the Ministry of Health and Welfare), development of photosensitive syndrome by eating of the internal organs of spring abalone and chlorella processed food is known. It is thought to be because pheophorbide and the like are delivered through blood to tissue cells in a living body and oxygen activated by light in the presence of this substance oxidizes a fatty acid (an arachidonic acid) and the like constituting the cell membrane so as to form lipid peroxide, and the lipid peroxide induces destruction of tissue cells of the biological membrane and other various disorders, or cause itching of the skin by increasing the permeability of the capillary vessels.
As guidelines regarding health foods in this field, the above-mentioned Notification by the Director of Environmental Health Bureau of the Ministry of Health and Welfare is known. It mentions that the existing pheophorbide amount should not exceed 100 mg %, or the total pheophorbide amount (the sum of the existing pheophorbide amount and the chlorophyllase activity) should not exceed 160 mg %.
The Notification by the Director of Environmental Health Bureau of the Ministry of Health and Welfare describes heat treatment as means of decreasing the total pheophorbide amount and the existing pheophorbide amount. However, such heat treatment poses such a problem of quality control that the contained β-carotene is easily oxidized and therefore degraded, resulting in a decrease in β-carotene contained in dried powder product.
In particular, in culture facilities used outside for commercial mass-culturing of the algae belonging to the genus Dunaliella, the liquid temperature increases due to an elevation of temperature in summer, and therefore the total pheophorbide amount and the existing pheophorbide amount in summer tend to be higher than those in winter. Since more sufficient heat treatment is required in summer than in winter, there has been a serious problem in quality control that β-carotene contained in a dried powder product is decreased.
The above-mentioned Japanese Patent Laid-Open No. 1997-203 certainly refers to a dried powder product of the algae belonging to the genus Dunaliella, but it does not refer to the above-mentioned problem in quality control regarding pheophorbide.
Furthermore, Japanese Patent Laid-Open No. 2001-161348 specifically refers to a method for producing a dried powder product of the algae belonging to the genus Chlorella, but it does not refer to the above-mentioned problem in quality control regarding pheophorbide.
Therefore, the present invention has an object to provide a method for producing a dried Dunaliella powder product containing β-carotene at a high concentration by suppressing the degradation of β-carotene as an active ingredient while decreasing a pheophorbide amount to a predetermined value or less in a step for producing a dried powder product even if the total pheophorbide amount and the existing pheophorbide amount of the cultured algae belonging to the genus Dunaliella are higher in summer.